Optically-controlled switching of power to downhole devices

ABSTRACT

A well having optically controlled switching, the well including a power cable run along a tubular string in a borehole, one or more downhole devices attached to the tubular string, one or more optically-controlled switches arranged downhole, where each switch is coupled between the power cable and one of the one or more downhole devices to enable or disable a flow of power to the downhole device, and a switch controller coupled to the one or more optically-controlled switches via an optical fiber, where each of the one or more optically-controlled switches are independently controllable.

BACKGROUND

Oilfield operators are faced with the challenge of maximizinghydrocarbon recovery within a given budget and timeframe. While theyperform as much logging and surveying as feasible before and during thedrilling and completion of production wells and, in some cases,injection wells, the information gathering process does not end there.It is desirable for the operators to track the movement of fluids in andaround the reservoirs, as this information enables them to adjust thedistribution and rates of production among the producing and/orinjection wells to avoid premature water breakthroughs and otherobstacles to efficient and profitable operation. Moreover, suchinformation gathering further enables the operators to better evaluatetreatment and secondary recovery strategies for enhanced hydrocarbonrecoveries.

To obtain such information, a permanent electromagnetic (EM) monitoringsystem may be attached to the casing string as it is run into theborehole. Example monitoring devices may include electrodes andelectromagnetic antennas. Power to the monitoring devices may beindependently controlled to enable maximum power delivery and easiermonitoring of individual device power consumption or, for example, todetermine independent device current leakage. If not properlydetermined, such leakage may be incorrectly interpreted as formationresistivity, thus resulting in inaccurate measurement determinations.

The independent power control may be accomplished by having a singlepower source and a switching unit at the Earth's surface and runningindependent power lines downhole to each of the monitoring devices.However, this consumes a great amount of limited space within theborehole, thus limiting the number of independent lines that may be run.This method also inherently increases cost due to the additional wirerequired to run each power source. Moreover, the increased hardwarerepresents additional points of failure within the system, may introduceadditional unwanted currents and/or voltage noise, and adds additionalhardware that must be accounted for so as not to be damaged whenperforming further downhole operations (e.g., perforating, hydraulicfracturing, or stimulation activities).

BRIEF DESCRIPTION OF THE DRAWINGS

Accordingly, there are disclosed herein systems and methods forcontrolling power to downhole devices via optical switching. In thedrawings:

FIG. 1 shows an illustrative permanent EM monitoring system for areservoir.

FIG. 2 is an enlarged schematic view of an illustrative opticallycontrolled well monitoring system.

FIG. 3 is a flow diagram of an illustrative method for controlling apermanent EM monitoring system.

It should be understood, however, that the specific embodiments given inthe drawings and detailed description thereto do not limit thedisclosure. On the contrary, they provide the foundation for one ofordinary skill to discern the alternative forms, equivalents, andmodifications that are encompassed together with one or more of thegiven embodiments in the scope of the appended claims.

DETAILED DESCRIPTION

Certain disclosed system and method embodiments provide an opticallycontrolled switching system for downhole devices. The system may includea tubular string having a power cable and one or more downhole devicesattached thereto and arranged within a borehole. One or moreoptically-controlled switches are arranged downhole, each of which iscoupled between one of the downhole devices and the power cable toenable or disable a flow of power to the downhole device. Additionally,a switch controller is optically coupled to the switches via an opticalfiber and independently controls each of the switches.

In some embodiments, exemplary downhole devices may include capacitiveelectrodes, galvanic electrodes, multi-loop antennas, and electricmotors (e.g., gauges, valves, and the like). The system may furtherinclude additional sensors, such as current and voltage sensors coupledto the switches and capable of measuring a current or voltage of thecorresponding downhole device. In further embodiments, the tubularstring may be a casing string, wherein the tubular string, power cable,and downhole devices are cemented within the borehole.

To provide some context for the disclosure, FIG. 1 shows an illustrativepermanent EM monitoring system 100 (hereinafter “system 100”). Asdepicted, the system 100 includes a well 102 having a casing string 106set within a borehole 104 of a formation 101 and secured in place by acement sheath 108. In alternative embodiments, the casing string 106 maybe a general tubular string. Moreover, the tubular string may beelectrically insulated.

Inside the casing string 106, a production tubing string 110 defines anannular flow path (between the walls of the casing string and theproduction tubing string) and an inner flow path (along the bore of theproduction tubing string). Wellhead valves 112 and 114 provide fluidcommunication with the bottom-hole region via the annular and inner flowpaths, respectively. Well 102 may function as a production well, aninjection well, or simply as a formation monitoring well.

The well 102 includes downhole devices 116 a-c (illustrated as a first,second, and third downhole device 116 a, 116 b, and 116 c, respectively)attached to the casing string 106 and cemented within the borehole 104.Example downhole devices may include, but are not limited to, capacitiveelectrodes, galvanic electrodes, multi-loop antennas, and electricmotors (e.g., gauges, valves, and the like). The downhole devices 116a-c receive power from a power source 118 via a power cable 120 strappedto the outside of the casing string 106. The power cable 120 may includea mono-conductor or multi-conductor core.

Interposed between the power cable 120 and each downhole device 116 a-cis an optically-controlled switch 122 a-c (depicted as a first, second,and third switch, 122 a, 122 b, and 122 c, accordingly) which enables ordisables the flow of power to the corresponding downhole device 116 a-c.

The switches 122 a-c are independently controllable via an optical fiber124 coupled to a switch controller 126. Advantageously, only a singlepower cable 120 and a single optical fiber 124 are required, thussubstantially saving space within the borehole and reducing oreliminating the problems of the prior art which may use individual powercables for each downhole device 116 a-c.

The switch controller 126 is coupled to and controlled by a processingunit 128 which may be, for example, a computer in tablet, notebook,laptop, or portable form, a desktop computer, a server or virtualcomputer on a network, a mobile phone, or some combination of likeelements that couple software-configured processing capacity to a userinterface 130. The processing unit 128 may perform processing includingcompiling a time series of measurements to enable monitoring of the timeevolution, and may further include the use of a geometrical model of thereservoir that takes into account the relative positions andconfigurations of the downhole devices 116 a-c to obtain one or moreparameters or formation characteristics. For example, if one of thedownhole devices 116 a-c is a dielectric measurement tool, thoseparameters may include a resistivity distribution and an estimated watersaturation.

The processing unit 128 may further enable the user to adjust theconfiguration of the system, for example, modifying such parameters asacquisition or generation rate of the downhole devices 116 a-c, firingsequence, transmit amplitudes, transmit waveforms, transmit frequencies,receive filters, and demodulation techniques. In some contemplatedsystem embodiments, the processing unit 128 further enables the user toadjust injection and/or production rates to optimize production from thereservoir.

FIG. 2 illustrates an enlarged schematic view of an optically controlledwell monitoring system 200 (hereinafter “system 200”). The system 200may be similar to the system 100 of FIG. 1 and therefore may be bestunderstood with reference thereto, where like numerals represent likeelements that will not be described again in detail. In particular, asdepicted, the system 200 includes three downhole devices 116 a-cattached to the casing string 106. The downhole devices 116 a-c receivepower from the power source 118 via the power cables 120 a-b (whereinpower cable 120 a is a source cable and power cable 120 b is a returncable). The three switches 122 a-c are interposed between each of thedownhole devices 116 a-c and the power cables 120 a-b, thereby enablingor disabling a flow of power to the associated downhole device 116 a-c.

The switches 122 a-c are controlled by the switch controller 126 andcoupled thereto via the optical fiber 124. One exemplary protocol thatmay be implemented over the optical fiber 124 enabling the switchcontroller 126 to independently control each switch 122 a-c isradio-over-fiber. When implementing such a protocol, the system 200 mayfurther include an optical modulator 202 for modulating the signal sentvia the optical cable to the switches 122 a-c. The modulated signal maybe received by a demodulator 204 a-c coupled to or integrated with theswitches 122 a-c for demodulating the optical signal and operating onlythe desired switch 122 a-c, thus enabling independent control of eachswitch 122 a-c.

As depicted, the downhole devices 116 a-c are electrodes which injectand receive current flowing through the formation 101. The first switch122 a has both contacts open, therefore the first electrode 116 neitherinjects nor receives current. The second switch 122 b has the contactassociated with the source power cable 120 a closed, thereby enablinginjection of current from the second electrode 116 b. The third switch122 c has one contact associated with the return power cable 120 bclosed, thereby enabling a return path for the current.

Advantageously, only a single power cable 120 is required (even though asource and return power cable 120 a and 120 b are depicted). This is asignificant reduction in cables, and thus space, required downhole.Moreover, the system requires less power than prior systems due to theswitches being optically operated rather than electrically operated.

In some embodiments, the optical fiber 124 may further serve to transmitdata from one or more sensors 206 (one shown) coupled to or integratedwith the switches 122 a-c to help monitor the system 200. As depicted,the sensor 206 is coupled to the second switch 122 b for measurements ofthe corresponding downhole device 116 a-c. For example, such sensors 206may include a current or voltage sensor that measures the current orvoltage of the downhole device 116 b. Alternatively, the sensor 206 maytake temperature or vibration measurements in proximity to the downholedevice 116 a-c. Advantageously, such a configuration may enable moreprecise measurements due to measuring individual downhole devices 116a-c, as compared to taking a single measurement near the power source118 and only obtaining overall system information.

FIG. 3 is a flow diagram of an illustrative permanent EM monitoringmethod 300. The method begins at block 302 with a crew coupling one ormore EM monitoring downhole devices and a power cable to a tubularstring. The power cable is coupled to a power source at or near theEarth's surface. Downhole devices may be, for example, electrodes or amulti-turn loop antenna. The crew further couples anoptically-controlled switch between each of the downhole devices and thepower cable. Of course, those skilled in the art will appreciate thatthe optically-controlled switch may alternatively be embedded with orpart of the downhole device circuitry and need not be a physicallyseparate attachment or hardware. The tubular string and equipmentattached thereto may then be run into a borehole and cemented thereinfor permanent monitoring.

At block 304, a well operator may control the flow of power to each ofthe downhole devices via the switches coupled between the downholedevices and the power cable. Moreover, as at block 306, the operator mayindividually control each of the switches with a switch controllercoupled thereto via an optical cable. Advantageously, only a singlepower cable and a single optical fiber are required, thus substantiallysaving space within the borehole and reducing or eliminating theproblems of the prior art which may use individual power cables for eachdownhole device 116 a-c.

The method 300 may further monitor characteristics of the downholedevices. For example, the method 300 may employ a current sensor coupledto the device to monitor the current generated or received by thedevice. Alternatively, voltage of the downhole device may be measuredusing voltage sensors. Advantageously, taking such measurements at eachdevice individually may provide the operator with more accurate anddetailed data as compared to merely monitoring the overall system nearthe power source. Additional measurements that may be taken are, forexample and without limitation, downhole temperature and vibrations.Such measurements may be conveyed to the surface via the optical fiber.The method 300 may utilize such measurements to determine a formationcharacteristic with a processor, such as formation resistivity.

Numerous other modifications, equivalents, and alternatives, will becomeapparent to those skilled in the art once the above disclosure is fullyappreciated. For example, similar application can be applied to wirelineresistivity logging, logging-while-drilling (LWD), electromagneticranging, and telemetry applications without departing from the scope ofthe present disclosure. It is intended that the following claims beinterpreted to embrace all such modifications, equivalents, andalternatives where applicable.

Embodiments disclosed herein include:

A: A well having optically controlled switching, the well including apower cable run along a tubular string in a borehole, one or moredownhole devices attached to the tubular string, one or moreoptically-controlled switches arranged downhole, where each switch iscoupled between the power cable and one of the one or more downholedevices to enable or disable a flow of power to the downhole device, anda switch controller coupled to the one or more optically-controlledswitches via an optical fiber, where each of the one or moreoptically-controlled switches are independently controllable.

B: A permanent electromagnetic (EM) monitoring method that includespositioning a tubular string having a power cable and one or moredownhole devices attached thereto in a borehole, controlling the flow ofpower to each of the downhole devices via one or moreoptically-controlled switches arranged downhole, wherein each switch iscoupled between one of the one or more downhole devices and the powercable, and controlling the one or more optically-controlled switcheswith a switch controller, the switch controller being coupled to the oneor more optically-controlled switches via an optical fiber, and whereineach of the one or more optically-controlled switches are independentlycontrollable

Each of embodiments A and B may have one or more of the followingadditional elements in any combination:

Element 1: At least one of the downhole devices includes a capacitiveelectrode. Element 2: At least one of the downhole devices includes agalvanic electrode. Element 3: At least one of the downhole devicesincludes a multi-turn loop antenna. Element 4: At least one of thedownhole devices is an electric motor. Element 5: The switch controlleris arranged at the surface. Element 6: An optical fiber current sensorcoupled to at least one of the optically-controlled switches thatmeasures a current of the corresponding downhole device. Element 7: Anoptical fiber voltage sensor coupled to at least one of theoptically-controlled switch that measures a voltage of the correspondingdownhole device. Element 8: Where the power cable is a multi-conductorcable. Element 9: Wherein the tubular string is electrically insulated.Element 10: Where the tubular string is a casing string cemented withinthe borehole. Element 11: A processing unit which determines a formationcharacteristic.

Element 12: Cementing the tubular string and downhole devices in theborehole. Element 13: Monitoring characteristics of the downholedevices. Element 14: Where the characteristic includes one of the groupof an electrical current, an electrical voltage, a temperature, or avibration. Element 15: Where the monitoring the electrical current isperformed by an optical fiber current sensor coupled to one of theoptically-controlled switches. Element 16: Where the monitoring theelectrical voltage is performed by an optical fiber voltage sensorcoupled to one of the optically-controlled switches. Element 17:Controlling one of a voltage, current, or waveform of the downholedevices with the corresponding optically-controlled switch. Element 18:Where one of the downhole devices is a multi-turn loop antenna, themethod further comprising measuring an electromagnetic signal with themulti-turn loop antenna. Element 19: Where one of the downhole devicesincludes an electric motor, the method further comprising controllingthe electric motor. Element 20: Further comprising determining aformation characteristic with a processing unit.

What is claimed is:
 1. A well having optically-controlled switching, thewell comprising: a power cable run along a tubular string in a borehole;one or more downhole devices attached to the tubular string; one or moreoptically-controlled switches arranged downhole, wherein each switch iscoupled between the power cable and one of the one or more downholedevices to enable or disable a flow of power to the downhole device; anda switch controller coupled to the one or more optically-controlledswitches via an optical fiber, wherein each of the one or moreoptically-controlled switches are independently controllable.
 2. Thewell of claim 1, wherein at least one of the downhole devices includes acapacitive electrode.
 3. The well of claim 1, wherein at least one ofthe downhole devices includes a galvanic electrode.
 4. The well of claim1, wherein at least one of the downhole devices includes a multi-turnloop antenna.
 5. The well of claim 1, wherein at least one of thedownhole devices is an electric motor.
 6. The well of claim 1, whereinthe switch controller is arranged at the surface.
 7. The well of claim1, further comprising an optical fiber current sensor coupled to atleast one of the optically-controlled switches that measures a currentof the corresponding downhole device.
 8. The well of claim 1, furthercomprising optical fiber voltage sensor coupled to at least one of theoptically-controlled switch that measures a voltage of the correspondingdownhole device.
 9. The well of claim 1, wherein the power cable is amulti-conductor cable.
 10. The well of claim 1, wherein the tubularstring is electrically insulated.
 11. The well of claim 1, wherein thetubular string is a casing string cemented within the borehole.
 12. Thewell of claim 1, further comprising a processing unit which determines aformation characteristic.
 13. A permanent electromagnetic (EM)monitoring method, comprising: positioning a tubular string having apower cable and one or more downhole devices attached thereto in aborehole; controlling the flow of power to each of the downhole devicesvia one or more optically-controlled switches arranged downhole, whereineach switch is coupled between one of the one or more downhole devicesand the power cable; and controlling the one or moreoptically-controlled switches with a switch controller, the switchcontroller being coupled to the one or more optically-controlledswitches via an optical fiber, and wherein each of the one or moreoptically-controlled switches are independently controllable.
 14. Themethod of claim 13, further comprising cementing the tubular string anddownhole devices in the borehole.
 15. The method of claim 13, furthercomprising monitoring characteristics of the downhole devices.
 16. Themethod of claim 15, wherein the characteristic includes one of the groupof an electrical current, an electrical voltage, a temperature, or avibration.
 17. The method of claim 16, wherein the monitoring theelectrical current is performed by an optical fiber current sensorcoupled to one of the optically-controlled switches.
 18. The method ofclaim 16, wherein the monitoring the electrical voltage is performed byan optical fiber voltage sensor coupled to one of theoptically-controlled switches.
 19. The method of claim 13, furthercomprising controlling one of a voltage, current, or waveform of thedownhole devices with the corresponding optically-controlled switch. 20.The method of claim 13, wherein one of the downhole devices includes amulti-turn loop antenna, the method further comprising measuring anelectromagnetic signal with the multi-turn loop antenna.
 21. The methodof claim 13, wherein one of the downhole devices includes an electricmotor, the method further comprising controlling the electric motor. 22.The method of claim 13, further comprising determining a formationcharacteristic with a processing unit.